Trucks that are used on model railroad rolling stock are scaled-down versions of prototypical railroad trucks. Although the framework for some trucks are formed as a one-piece structure, most trucks used by serious model railroaders include a separate truck bolster and spaced-apart side frames, wherein the bolsters are held in the side frames by means of springs, which allow a side frame to move torsionally relative to the bolster and to the other side frame. Wheel sets for each truck, including an axle having a wheel at each end thereof, are contained within journal boxes, which are located in the side frames. The flexible nature of the multi-piece truck allows the wheel sets to follow irregularities in the track, thereby maintaining the truck, and in turn, the rolling stock, on the track.
Known flexible trucks are quite difficult to assemble because the springs, which hold the truck elements together, are essentially free-floating, i.e., they are not secured to either the bolster or the side frame, and are usually captured to prevent lateral movement of the springs by protrusions which extend from the bolster and side frames. The springs used in both prototypical and model railroad trucks are usually coil springs, which extend between the end of a bolster and a truck side frame. In some instances, leaf springs may be used in prototypical trucks. Coil springs used in model railroad trucks are typically less than 0.16 cm in diameter and approximately 0.3 cm in non-compressed length. They are most difficult to handle. Although the use of a specialized pics may assist a model railroader with the insertion of springs into a truck assembly, the assembly of a conventional truck still requires that each individual spring be placed between the bolster and side frame. Generally, four springs are provided, two associated with each end of the bolster. Such assembly does not lend itself to any type of automation, and further, requires delicate manual assembly of the truck assembly, a task which produces stress in the hands and eyes of the assembly worker, and also results in increased manufacturing costs. Examples of a truck and an assembly technique which eliminate some of these concerns are found in U.S. Pat. No. 5,768,999 for Model Railroad Truck, granted to Edwards on Jun. 23, 1998, and U.S. Pat. No. 5,832,837 for Method of Assembling a Model Railroad Truck, granted to Edwards on Nov. 10, 1998.
Springs as provided on model railroad trucks provide for torsional movement of a truck side frame relative to a truck bolster, but do not really compress to provide cushioning for the rolling stock to which they are mounted. Torsion from side-to-side of a truck is important to enable the truck to pass over uneven trackwork, frogs and switch points. One solution used is to provide wheel sets with larger-than-scale flanges on the wheels, however this is highly objectionable to the serious model railroader. Another problem inherent in conventional sprung trucks is side frame toe out, which can actually lead to derailment.
Perhaps the most serious objection to the use of discrete springs in model railroad trucks is that the springs are not to scale. A prototype truck may have two or more large coil springs, or plural leaf springs, located between the bolster and the side frame, however, such springs are massive, and likely have a cross section of between two and three inches. The coil springs used on models are much finer, and, if converted to prototype scale, would have a diameter of less than half an inch, and would be non-functional in a prototypical world at this size.